Surge protective device with abnormal overvoltage protection

ABSTRACT

Surge protective devices having surge protective and overvoltage protection capability are provided. In one example embodiment, the surge protective device can include a surge protection circuit. The surge protection device can include an overvoltage protection circuit coupled in series with the surge protection circuit. The overvoltage protection circuit can include a voltage sensing circuit associated with a voltage threshold, one or more switching elements, and/or a gating circuit coupled to the voltage sensing circuit. The gating circuit can be configured to control the one or more switching elements to be in a non-conducting state when the voltage sensing circuit detects a voltage that exceeds the voltage threshold.

The present application is a 371 of International Application No.PCT/US2016/055903 filed on Oct. 7, 2016, which claims priority to U.S.Provisional Application No. 62/326,234 filed on Apr. 22, 2016 and U.S.Provisional Application No. 62/238,915 filed on Oct. 8, 2015, which isincorporated herein in its entirety by reference thereto.

FIELD

The present disclosure relates generally to surge protective devices,and more particularly to surge protective devices that can provideabnormal overvoltage protection.

BACKGROUND

Surge protective devices can be used to assist in protecting loads fromelectrically induced damage. Surge protective devices are typicallydesigned to deal with short duration, high magnitude voltage and/orcurrent events on the electrical wiring system. These events can lastfrom several microseconds to several milliseconds and can beattributable to, for instance, switching loads on and off, lightningstrikes, equipment failures, faults, etc. A surge protective device canabsorb these events by clamping them to more manageable magnitudes. Inthis process, a surge protective device can heat up and eventually wearout.

There can be other events that can occur in an electrical system thatcan negatively affect load life and that may not be mitigated by a surgeprotective device. For example, an electrical system can exhibit voltagesags or swells. Electrical systems typically exhibit non-linear,reactive characteristics that can cause various undervoltage events,overvoltage events, oscillations, and/or some combination thereof whichcan be transient or even of longer term duration. One detrimental eventcan be a long duration, abnormal overvoltage condition, (e.g., swell).Loads are rated for operation on an electrical wiring supply and systemat a particular nominal voltage, but usually are specified to work in atolerance range around the nominal voltage. Experiencing an overvoltagecondition for an extended period of time above the high side tolerancecan cause some loads to be damaged.

SUMMARY

Aspects and advantages of embodiments of the present disclosure will beset forth in part in the following description, or may be learned fromthe description, or may be learned through practice of the embodiments.

One example aspect of the present disclosure is directed to a surgeprotective device. The surge protective device can include a surgeprotection circuit. The surge protective device can include anovervoltage protection circuit. The overvoltage protection circuit canbe coupled in series with the surge protection circuit. The overvoltageprotection circuit can include a voltage sensing circuit (e.g., a stringof one or more Zener diodes or other voltage sensing circuit) associatedwith a voltage threshold. The overvoltage protection circuit can includeone or more switching elements. The overvoltage protection circuit caninclude a gating circuit coupled to voltage sensing circuit. The gatingcircuit can be configured to control the one or more switching elementsto be in a non-conducting state when the voltage sensing circuit detectsa voltage that exceeds the voltage threshold. The gating circuit can beconfigured to control the one or more switching elements to be in aconducting state when the voltage sensing circuit detects a voltage thatdoes not exceed the voltage threshold.

Another example aspect of the present disclosure is directed to a surgeprotective device for a lighting system. The surge protective device caninclude a surge protection circuit. The surge protective device caninclude an overvoltage protection circuit coupled in series with thesurge protection circuit. The overvoltage protection circuit can includea relay configured to operate in a normally closed position. Theovervoltage protection circuit can include a bridge rectifier. Theovervoltage protection circuit can include a first circuit sectioncoupled to the bridge rectifier and the relay. The first circuit sectioncan be configured to control operation of the relay based on anovervoltage detection signal. The overvoltage protection circuit caninclude a second circuit section. The second circuit section can becoupled to the bridge rectifier and the first circuit section. Thesecond circuit section can be configured to provide the overvoltagedetection signal. The first circuit section can be configured to controlthe relay to be in an open state when the overvoltage detection signalis indicative of an overvoltage condition.

Another example aspect of the present disclosure can include a surgeprotective device. The surge protective device can include surgeprotection means for protecting a load from a short duration, highmagnitude transient condition. The surge protective device can includeovervoltage protection means for protecting the load from an overvoltagecondition.

Other example aspects of the present disclosure are directed tocircuits, devices, systems, and methods for providing overvoltageprotection for one or more loads.

These and other features, aspects and advantages of various embodimentswill become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the present disclosure and, together with thedescription, serve to explain the related principles.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed discussion of embodiments directed to one of ordinary skill inthe art are set forth in the specification, which makes reference to theappended figures, in which:

FIG. 1 depicts a block diagram of an example surge protective deviceaccording to example embodiments of the present disclosure;

FIG. 2 depicts a circuit diagram of an example surge protection circuitaccording to example embodiments of the present disclosure;

FIG. 3 depicts a circuit diagram of an example surge protection circuitaccording to example embodiments of the present disclosure;

FIG. 4 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure;

FIG. 5 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure;

FIG. 6 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure;

FIG. 7 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure;

FIG. 8 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure;

FIG. 9 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure;

FIG. 10 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure; and

FIG. 11 depicts a circuit diagram of an example overvoltage protectioncircuit according to example embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments, one or moreexamples of which are illustrated in the drawings. Each example isprovided by way of explanation of the embodiments, not limitation of thepresent disclosure. In fact, it will be apparent to those skilled in theart that various modifications and variations can be made to theembodiments without departing from the scope or spirit of the presentdisclosure. For instance, features illustrated or described as part ofone embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that aspects of the presentdisclosure cover such modifications and variations.

Example aspects of the present disclosure are directed to surgeprotective devices that combine surge protective functionality withabnormal overvoltage detection and shutdown capability. Moreparticularly, a surge protective device can include a surge protectioncircuit and an overvoltage protection circuit. The surge protectioncircuit can be configured to protect loads from high magnitude shortduration transient conditions and power surges. The overvoltageprotection circuit can be configured to protect the load from lowermagnitude, but perhaps longer duration, overvoltage conditions. In someembodiments, the surge protection circuit can protect loads from avoltage condition associated with a first magnitude and the overvoltageprotection circuit can protect loads from a voltage condition associatedwith a second magnitude. In some embodiments, the first magnitude can begreater than the second magnitude, such as at least two times greaterthan the second magnitude, such as at least ten times greater than thesecond magnitude. The surge protection circuit and the overvoltageprotection circuit can be included within the same housing or module.

According to example aspects of the present disclosure, the surgeprotection circuit can include one or more surge protection elementssuch as one or more fuses, breakers, metal oxide varistors (MOVs), gasdischarge tubes, Zener diodes, transient voltage suppression (TVS)diodes, thyristors, electrostatic discharge protection devices, and/orother surge protection elements. The surge protective elements can beconfigured to absorb short duration power surges and/or can beconfigured to disconnect power from the load during short duration powersurges. In some embodiments, the surge protection circuit can includeMOVs coupled between a first AC line and a second AC line as well asbetween the first AC line and a reference (e.g., ground reference) andthe second AC line and the reference. Fuse elements can be coupled inseries with one or more of the MOVs to provide additional surgeprotection capability.

The overvoltage protection circuit can be coupled in series with thesurge protection circuit. The overvoltage protection circuit can includeone or more switching elements, such as one or more transistors (e.g.,MOSFETs), one or more relays, or other suitable switching elements. Theone or more switching elements can be controlled to be normally in aconducting state to conduct power to a load. A voltage sensing circuit(e.g., a string of one or more Zener diodes or other voltage sensingcircuit) can be coupled to a gating circuit. Upon the occurrence of anovervoltage condition, the voltage sensing circuit can trigger operationof the gating circuit to control the one or more switching elements tobe in a non-conducting state. When in the non-conducting state, theovervoltage protection circuit can disconnect power from the load.

The one or more switching elements can remain in the non-conductingstate until the overvoltage condition has terminated. At this point, thevoltage sensing circuit can trigger the gating circuit to cause the oneor more switching elements to return to a conducting state and todeliver power to the load. In this way, the overvoltage protectioncircuit can prevent damage to the load resulting from lower magnitudeovervoltage conditions.

FIG. 1 depicts a block diagram of an example surge protective device 100according to example embodiments of the present disclosure. As shown,the surge protective device 100 can receive input power from a powersource 110. The power source 110 can be any suitable power source, suchas a single phase AC power source, multiphase AC power source (e.g.,three-phase power source), DC power source, or other suitable powersource. In one example implementation, the power source is a singlephase AC power source having a first AC line associated with a first ACpotential (positive or negative AC voltage) and a second AC lineassociated with a second AC potential (e.g., a neutral).

The surge protective device 100 can be coupled between the power source110 and a load 120. The load 120 can be any suitable load that drawspower from the power source 110, such as one or more lighting systems orother suitable loads. The surge protective device 100 can include asurge protection circuit 200 that is coupled in series with anovervoltage protection circuit 300.

In some embodiments, the surge protection circuit 200 can be surgeprotection means for protecting the load 120 from high magnitude shortduration transient conditions and power surges. The surge protectionmeans can include any of the surge protection circuits 200 disclosedherein, including the surge protection circuits 200 shown in FIGS. 2 and3 and equivalents thereof.

In some embodiments, the overvoltage protection circuit 300 can beovervoltage protection means for protecting protect the load 120 fromlower magnitude, longer duration overvoltage conditions. The overvoltageprotection means can include any of the overvoltage protection circuits300 disclosed herein, including the overvoltage protection circuits 300shown in FIGS. 4-11 and equivalents thereof.

FIG. 2 depicts a circuit diagram of one example surge protection circuit200 according to example embodiments of the present disclosure. Thesurge protection circuit 200 can receive power from a single phase ACpower source in the form a first AC line input 202 and a second AC lineinput 204. The first AC line input 202 can be associated with a first ACpotential (e.g., +120 V, −120 V, etc.) and the second AC line input 204can be associated with a second AC potential (e.g., 120 V, −120V, 0V,etc.). In some embodiments, the first AC line input 202 is associatedwith a positive or negative AC potential and the second AC line input204 is associated with a neutral. A reference 205 (e.g., a groundreference) can also be included as part of the input to the surgeprotection circuit 200.

The surge protection circuit 200 can provide a first AC input 212 and asecond AC input 214 to the overvoltage protection circuit 300. Similarto the AC line inputs 202 and 204, the first AC input 212 can beassociated with a first AC potential (e.g., +120 V, −120 V, etc.) andthe second AC input 204 can be associated with a second AC potential(e.g., 120 V, −120V, 0V, etc.). In some embodiments, the first AC input212 is associated with a positive or negative AC potential and thesecond AC input 214 is associated with a neutral.

The surge protection circuit 200 includes surge protective elementscoupled between each of the respective AC line inputs and/or thereference. For instance, as shown in FIG. 2, the surge protectioncircuit 200 includes a first MOV 210 coupled between the first AC lineinput 202 and the reference 205. The surge protection circuit 200includes a second MOV 220 coupled between the second AC line input 204and the reference 205. The surge protection circuit 200 includes a thirdMOV 230 coupled between the first AC line input 202 and the second ACline input 204.

The first MOV 210 can provide protection by clamping AC voltage duringcurrent surges between the first AC line 202 and the reference 205. Thesecond MOV 220 can provide protection by clamping AC voltage duringcurrent surges between the second AC line 204 and the reference 205. Thethird MOV 230 can provide protection by clamping AV voltages duringcurrent surges between the first AC line 202 and the second AC line 204.

The surge protection circuit 200 is discussed with reference to MOVsurge protective elements for purposes of illustration and discussion.Those of ordinary skill in the art, using the disclosures providedherein, will understand that other surge protective elements can be usedwithout deviating from the scope of the present disclosure, such asfuses, breakers, gas discharge tubes, Zener diodes, TVS diodes,thyristors, electrostatic discharge protection devices, and/or othersurge protection elements

In some embodiments, the surge protection circuit 200 can include othersurge protective elements to provide additional surge protectioncapability. For instance, as shown in FIG. 2, the surge protectioncircuit 200 can include a fuse 240 coupled in series with first AC lineinput 202. The fuse 240 can be configured to open when a current higherthan a fuse rating of the fuse 240 passes through the fuse 240.

FIG. 3 depicts a surge protection circuit 200 according to exampleembodiments of the present disclosure. The surge protection circuit 200of FIG. 3 is similar to the surge protection circuit of FIG. 2 exceptthat the surge protection circuit 200 of FIG. 3 includes an additionalfuse 250 coupled in series with the first MOV 210 and an additional fuse260 coupled in series with the second MOV 220. In addition, the surgeprotection circuit 200 includes a light emitting diode (LED) 270 thatcan be configured to emit light as an indicator when the surgeprotective circuit 200 is operational to protect a load from transientconditions.

FIG. 4 depicts a circuit diagram of an example overvoltage protectioncircuit 300 according to example embodiments of the present disclosure.The overvoltage protection circuit 300 can receive AC power from thesurge protection circuit 200 via AC input 212 and the AC input 214. Theovervoltage protection circuit 300 includes a voltage sensing circuitthat includes a string of Zener diodes 310. The overvoltage protectioncircuit 300 further includes a pair of switching elements 320 and 330.The pair of switching elements 320 and 330 can be configured to benormally in a conducting state so that power flows from the AC inputs212, 214 to the load via outputs 312 and 314. The string of Zener diodes310 can be coupled to a gating circuit 340. The gating circuit 340 cancontrol operation of the switching elements 320 and 330 based on thevoltage across the string of Zener diodes 310. For instance, when avoltage across the string of Zener diodes 310 exceeds a threshold level,the gating circuit 340 can control the switching elements 320 and 330 tobe in a non-conducting state so that power does not flow from the ACinputs 212, 214 to the load via outputs 312 and 314.

More particularly, the overvoltage protection circuit 300 of FIG. 4includes a string of Zener diodes 310 coupled between the AC input 212and the AC input 214. Diodes D1 and D2 can be coupled series with thestring of Zener diodes 310 so that the Zener diodes act on a half cycle(e.g., a positive cycle) of the AC power. The string of Zener diodes 310can be configured to block current when the voltage between AC input 212and AC input 214 is less than a threshold level. More particularly, eachof the Zener diodes in the string of Zener diodes 310 can provide ablocking voltage capability up to a certain voltage blocking threshold.Coupling the Zener diodes in series can increase this blocking voltagecapability. The amount and type of Zener diodes coupled in series can beselected to provide overvoltage protection up to a desired overvoltageprotection threshold. The overvoltage protection threshold can be lessthan a magnitude of a voltage protection capability provided by thesurge protection circuit 200.

Three Zener diodes are illustrated in the example embodiment of FIG. 4.Those of ordinary skill in the art, using the disclosures providedherein, will understand that more or fewer Zener diodes can be used inthe string of Zener diodes 310 without deviating from the scope of thepresent disclosure.

The overvoltage protection circuit 300 further includes a firstswitching element 320 and a second switching element 330 coupled betweenthe AC input 212 and the AC output 312. The first and second switchingelements 320 and 330 can include MOSFET devices. In the exampleembodiment of FIG. 3, a drain of the first MOSFET switching element 320can be coupled to the AC input 212 while the source of the first MOSFETswitching element 320 and be coupled to the source of the second MOSFETswitching element 330. The drain of the second MOSFET switching element330 can be coupled to the load (e.g., via the AC output 312). The gateof the first MOSFET switching element 320 and the second MOSFETswitching element 330 can be coupled to a gating circuit 340.

In the example embodiment of FIG. 4, the gating circuit 340 includes abipolar junction transistor (BJT) switching element 342. Other suitableswitching elements can be used in place of a BJT without deviating fromthe scope of the present disclosure, such as other suitable transistors.A base of the BJT switching element 342 is coupled to the string ofZener diodes 310. The gates of the MOSFET switching elements 320 and 330are coupled to an emitter of the BJT switching element 342. In addition,resistors R1 and R2 are coupled to the emitter of the BJT switchingelement 342.

The gating circuit 340 is operable to control the MOSFET switchingelements 320 and 330 to be normally in a conducting state to conductpower to the load. When an overvoltage condition occurs (e.g., when ablocking voltage capability of the Zener diodes is exceeded), the gatingcircuit 340 can be operable to control the MOSFET switching elements 320and 330 to be in a non-conducting state to prevent power from beingdelivered to the load.

More particularly, the string of Zener diodes 310 can be operable toblock current when the voltage of the AC input 212 does not exceed theblocking voltage capability of the string of Zener diodes 310. As aresult, little to no current flows through resistor R3 and a voltageless than a turn on voltage is applied to the base of the BJT switchingelement 342 to operate the BJT switching element 342 in a non-conductingstate. In this state, a gate voltage is applied to the gates of theMOSFET switching elements 320 and 330 sufficient to maintain the MOSFETswitching elements 320 and 330 in a conducting state.

During an overvoltage condition when the AC voltage exceeds the blockingvoltage capability of the string of Zener diodes 310, a current flowsthrough the string of Zener diodes 310 and resistor R3 resulting in ahigher voltage being applied to the base of the BJT switching element342. This will operate the BJT switching element 342 in a conductingstate. In this state, the gate voltage applied to the gates of the firstMOSFET switching element 320 and the second MOSFET switching element 330will be reduced, causing the first MOSFET switching element 320 and thesecond MOSFET switching element 330 to operate in a non-conductingstate. AC power is not conducted to the load when the first MOSFETswitching element 320 and the second MOSFET switching element 330 areoperated in the non-conducting state.

When the overvoltage condition ceases to exist and the voltage betweenAC input 212 and AC input 214 is less than the blocking voltagecapability of the string of Zener diodes 310, the current flowingthrough the string of Zener diodes 310 can be limited. This will reducethe voltage applied to the base of the BJT switching element 342 andwill operate the BJT switching element 342 in a non-conducting state. Inthis state, a gate voltage will be applied to the MOSFET switchingelements 320 and 330 to operate the MOSFET switching elements 320 and330 in a conducting state so that power can be delivered to the load.

Variations and modifications can be made to the example overvoltageprotection circuit 300 without deviating from the scope of the presentdisclosure. For instance, switching elements other than MOSFET switchingelements 320 and 330 can be controlled to deliver power to the loadbased on the existence of an overvoltage condition. In addition, thegating circuit 340 can include additional and/or alternative elements tocontrol the switching elements to selectively deliver power to the loadbased on the existence of an overvoltage condition.

For example, FIG. 5 depicts an overvoltage protection circuit 300according to another example embodiment of the present disclosure. Theovervoltage protection circuit 300 of FIG. 5 is similar to that depictedin FIG. 4. However, the overvoltage protection circuit 300 of FIG. 5includes an additional diode D3 and additional resistors R4 and R5 toprovide, for instance, additional stability to the overvoltageprotection circuit 300. The diode D3 can be used to limit the gatesource voltage of the MOSFET switching elements 320 and 330. Theresistor R4 can be coupled to the base of the BJT switching element 342to limit base emitter current of the BJT switching element 342. Theresistor R5 can be coupled to the emitter of the BJT switching element342 to limit current through diode D2. Other components can be used inthe overvoltage protection circuit without deviating from the scope ofthe present disclosure.

FIG. 6 depicts an example overvoltage protection circuit 300 accordingto yet another example embodiment of the present disclosure. Theovervoltage protection circuit 300 includes a string of Zener diodes 310and MOSFET switching elements 320 and 330. The MOSEFET switchingelements 320 and 330 can be configured to be normally in a conductingstate so that power flows from the AC inputs 212, 214 to the load viaoutputs 312 and 314. The string of Zener diodes 310 can be coupled to agating circuit 340. The gating circuit 340 can control operation of theswitching elements 320 and 330 based on the voltage across the string ofZener diodes 310. For instance, when a voltage across the string ofZener diodes 310 exceeds a threshold level, the gating circuit 340 cancontrol the switching elements 320 and 330 to be in a non-conductingstate so that power does not flow from the AC inputs 212, 214 to theload via outputs 312 and 314.

The gating circuit 340 of FIG. 6 can include an optocoupler 350. Theoptocoupler 350 can be configured to apply an output voltage based atleast in part on light emitted by a light emitting diode in theoptocoupler 350. The state of the optocoupler 350 can be used to controlthe state of the MOSFET switching elements 320 and 330.

More specifically, the string of Zener diodes 310 can receive AC powerthrough rectifier diodes D1, D2, D3, and D4. When the AC voltage doesnot exceed the blocking voltage capability of the string of Zener diodes310, the optocoupler 250 provides no signal to the gates of the MOSFETswitching elements 320 and 330 leaving the MOSFET switching elements 320and 330 in a normal conducting state so that power can be delivered tothe load. During an overvoltage condition, when the AC voltage exceeds ablocking voltage capability of the string of Zener diodes 310, currentcan flow through Zener diodes 310 and resistor R6, activating theoptocoupler 350. In this state, the MOSFET switching elements 320 and330 are controlled to be in a non-conducting state so that power is notdelivered to the load. The MOSFET switching elements 320 and 330 canremain in this state until the overvoltage condition has ceased to existand the AC voltage no longer exceeds a blocking voltage capability ofthe string of Zener diodes 310. Variations and modifications can be madeto this example overvoltage protection circuit 300 without deviatingfrom the scope of the present disclosure.

For instance, FIG. 7 depicts an overvoltage protection circuit 300having a gating circuit 340 that includes an optocoupler 350 accordingto example embodiments of the present disclosure. The overvoltageprotection circuit 300 of FIG. 7 is similar to that of FIG. 6, exceptthat the overvoltage protection circuit 300 of FIG. 7 additionallyincludes a current regulator 360 coupled in series with the optocoupler350. The current regulator 360, in conjunction with resistors R6 and R7,can be used to limit current through the Zener diodes 310 and theoptocoupler 350. The current regulator 360 can be a constant currentregulator that may or may not be adjustable.

In one embodiment, the current regulator 360 can be a switchable currentregulator having a gate terminal, a positive terminal, and a negativeterminal. The gate terminal can be coupled to resistor R7. The positiveterminal can be coupled to the optocoupler 350. The negative terminalcan be coupled to the AC input 214 through diode D2. In one embodiment,the current regulator 360 is an IXCP 10M45S current regulatormanufactured by IXYS Corporation.

In the example embodiment of FIG. 7, the gating circuit 340 additionallyincludes capacitors C1 and C2, diode D5, and resistor R8 to provide, forinstance, additional stability to the gating circuit 340. Additionally,the overvoltage protection circuit 300 can include an LED circuit. TheLED circuit can include an LED 370 coupled in series with a diode D6 anda resistor R8. The LED 370 can be configured to emit light when theMOSFET switching elements 320 and 330 are in a conducting state. The LED370 can be configured to not emit light when the MOSFET switchingelements 320 and 330 are not in the conducting state. In this way, theLED circuit can provide an indicator as to whether the overvoltageprotection circuit 300 is delivering power to the load or not deliveringpower to the load.

FIG. 8 depicts an overvoltage protection circuit 300 according to yetanother example embodiment of the present disclosure. The overvoltageprotection circuit 300 is similar to that of FIG. 7 except that theovervoltage protection circuit 300 of FIG. 8 replaces the currentregulator 360 with a current limiting circuit 380. The current limitingcircuit 380 includes a MOSFET, BJT, and Zener diode to provide currentlimiting functionality for the string of Zener diodes 310 and theoptocoupler 350.

The example overvoltage protection circuits 300 of FIGS. 4-8 have usedMOSFET switching elements 320 and 330 to control the delivery of powerto the load based on overvoltage conditions. Those of ordinary skill inthe art, using the disclosures provided herein, will understand thatother switching elements can be used without deviating from the scope ofthe present disclosure. For instance, one or more relays can be used asswitching elements to control the delivery of power to the load based onthe presence of an overvoltage condition without deviating from thescope of the present disclosure.

FIG. 9 depicts one example overvoltage protection circuit 300 thatincludes a relay switching element 380 that can be controlled to deliverpower to the load based on an overvoltage condition. More particularly,overvoltage protection circuit 300 includes a string of Zener diodes 310and a relay switching element 380. The relay switching element 380 canbe configured to be normally in a conducting state so that power flowsfrom the AC inputs 212, 214 to the load via outputs 312 and 314. Thestring of Zener diodes 310 can be coupled to a gating circuit 340.

The gating circuit 340 can control operation of the relay switchingelement 380 based on the voltage across the string of Zener diodes 310.For instance, when a voltage across the string of Zener diodes 310exceeds a threshold level, the gating circuit 340 can energize a coil290 causing the relay switching element 390 to be in a non-conductingstate so that power does not flow from the AC inputs 212, 214 to theload via outputs 312 and 314. When the overvoltage condition has ceasedto exist and the voltage across the string of Zener diodes 310 no longerexceeds the voltage blocking capability of the string of Zener diodes310, the gating circuit 340 can de-energize the coil 390. In this state,the relay switching element 380 can conduct AC power to the load. Asshown, the gating circuit 340 can include various combinations of BJTs,Zener diodes, and MOSFETS to provide current limiting functionality aswell as to energize coil 390 based on the voltage across the string ofZener diodes 310.

FIG. 10 depicts an overvoltage protection circuit 300 according toanother example embodiment of the present disclosure. The overvoltageprotection circuit 300 can include a relay switching element 380configured to be normally in a conducting state so that power flows fromthe AC inputs 212, 214 to the load via outputs 312 and 314. Theovervoltage protection circuit 300 further includes a voltage sensingcircuit 310 and a gating circuit 340. When the voltage sensed at thevoltage sensing circuit 310 exceeds a threshold, the gating circuit 340can control relay switching element 380 to be in a non-conducting stateto provide overvoltage protection for the load.

More particularly, the overvoltage protection circuit 300 of FIG. 10includes a conditioning circuit 392. The conditioning circuit 392 caninclude various elements (e.g., capacitors, diodes, resistors, etc.) togenerate a power supply for various components of the overvoltageprotection circuit 300. For instance, the conditioning circuit cangenerate a voltage Vcc to power various components of the overvoltageprotection circuit 300.

The voltage sensing circuit 310 can include a voltage divider formed byresistors R10 and R11. The voltage divider can provide a sensed voltageto comparator circuit 334. Comparator circuit 334 can be coupled tovoltage Vcc. The comparator circuit 334 can also receive an input from avoltage reference circuit 336 configured to generate a voltage referenceVref corresponding to a voltage threshold. The voltage reference circuit336 can be an integrated circuit or other suitable circuit that can beprogrammed or otherwise configured to provide a constant voltagereference Vref. The voltage reference circuit 336 can also be coupled toVcc.

The gating circuit 340 can include an optocoupler 350 and a switchingelement 342 (e.g., a MOSFET). The comparator circuit 334 can compare thesensed voltage from the voltage divider formed by resistors R10 and R11with the voltage reference Vref. When the sensed voltage does not exceedthe voltage reference, the optocoupler 350 can provide no signal to thegate of the switching element 342. In this state, a coil 390 associatedwith relay switching element 380 is not energized and the relayswitching element 380 remains in the normally conducting state.

When the sensed voltage does exceed the voltage reference, theoptocoupler 350 can provide a signal to activate the switching element342 (e.g., providing a gate signal to a gate of the MOSFET) causing thecoil 390 to become energized. The energized coil 390 can open the relayswitching element 380 causing the relay switching element 380 to be in anon-conducting state for as long as the sensed voltage exceeds thevoltage reference Vref. In this way, the overvoltage protection circuit300 of FIG. 10 provides overvoltage protection for a load.

FIG. 11 depicts a circuit diagram of an overvoltage protection circuitaccording to example embodiments of the present disclosure. The surgeprotection circuit 200 includes components Z1, Z2, Z3 D1, Led1, and R1.The overvoltage protection circuit 300 includes all other components.

The overvoltage protection circuit 300 is based on a relay 380 in thenormally closed position waiting for a detection of overvoltage in whichthe relay 380 is activated and the line connection is opened, turningoff power to the load. This logic was chosen so that the device wouldreset itself when the overvoltage condition is no long present. This canreduce any issues of expected switching life since the relay 380 doesnot have to switch every time the power is turned on. The line voltageon the input to the relay is sampled at bridge rectifier BR1. Off of BR1main rectifier are two main circuit sections.

The first circuit section is a relay power circuit section adjusted toprovide the correct voltage and power to the control coil of the relay380. The first circuit section includes R3, R4, and Zener diode D4. Therelay coil can require, for instance, 110V to operate and therefore D4can be a 100V Zener diode. D5 and C2 represent a peak detection and bulkstorage for control power for the relay control coil. D9 is across therelay control coil itself to clamp stored energy in the relay coil whenturned off. The first circuit section further includes Q1, Q2, R7, R8,R9, and R10 and represents the switch circuit of the power circuit whichprovides for the turning on or off of the relay 380. Q1 is a firstswitching element (e.g., a MOSFET) that acts as the main switchconfigured with second switching element Q2 (e.g. a MOSFET) to work as adiscrete Schmidt trigger with resistors R9 and R10 providing somehysteresis between the switching on and off based on the detectionsignal.

The second circuit section off of BR1 is the overvoltage detectionsignal circuit. The overvoltage detection signal circuit can includeresistor R2 and Zener diodes D2, D3 and D7. The overvoltage detectionsignal circuit can include components C3, R6 and D8 provide filteringand protection for the gate circuit of Q1 which is the input voltage tothe Schmidt trigger. When the peak voltage of the line is high enoughthe detection circuit allows for Q1 to turn on and activate the relay.

There is also an indicator circuit consisting of D10, Led2, and R11connected to the normally open pole of the relay. If the relay does opendue to a detected voltage in excess of the Zener set points in thedetection signal circuitry, line voltage is switched to the indicationcircuit providing a visual indicator the device is in overvoltageprotection mode.

While the present subject matter has been described in detail withrespect to specific example embodiments thereof, it will be appreciatedthat those skilled in the art, upon attaining an understanding of theforegoing may readily produce alterations to, variations of, andequivalents to such embodiments. Accordingly, the scope of the presentdisclosure is by way of example rather than by way of limitation, andthe subject disclosure does not preclude inclusion of suchmodifications, variations and/or additions to the present subject matteras would be readily apparent to one of ordinary skill in the art.

What is claimed is:
 1. A surge protective device, comprising: a surgeprotection circuit comprising one or more surge protective elementscoupled between a first AC line input and a second AC line input, one ormore surge protective elements coupled between the first AC line inputand a reference, and one or more surge protective elements coupledbetween the second AC line input and the reference; an overvoltageprotection circuit coupled in series with the surge protection circuit,the overvoltage protection circuit including: a voltage sensing circuitassociated with a voltage threshold; one or more switching elements; anda gating circuit coupled to the voltage sensing circuit; wherein thegating circuit is configured to control the one or more switchingelements to be in a non-conducting state when the voltage sensingcircuit detects a voltage that exceeds the voltage threshold.
 2. Thesurge protective device of claim 1, wherein the gating circuit isconfigured to control the one or more switching elements to be in aconducting state when the voltage sensing circuit detects a voltage thatdoes not exceed the voltage threshold.
 3. The surge protective device ofclaim 1, wherein the voltage sensing circuit comprises a string of Zenerdiodes.
 4. The surge protective device of claim 3, wherein the voltagethreshold corresponds to a voltage blocking threshold associated withthe string of Zener diodes.
 5. The surge protective device of claim 1,wherein the one or more switching elements comprise a plurality ofMOSFET switching elements.
 6. The surge protective device of claim 1,wherein the one or more switching elements comprise a relay switchingelement.
 7. The surge protective device of claim 3, wherein the gatingcircuit comprises a bipolar junction transistor switching element. 8.The surge protective device of claim 7, wherein the string of one ormore Zener diodes is coupled to the base of the bipolar junctiontransistor switching element.
 9. The surge protective device of claim 1,wherein the gating circuit comprises an optocoupler.
 10. The surgeprotective device of claim 1, wherein the gating circuit comprises acurrent regulator.
 11. The surge protective device of claim 1, whereinthe gating circuit comprises a current limiting circuit.
 12. The surgeprotective device of claim 1, wherein the surge protective elementscomprise metal oxide varistors.
 13. The surge protective device of claim1, wherein the surge protection circuit is configured to withstand avoltage from a 480V three phase power source.
 14. A surge protectivedevice for a lighting system, the surge protective device comprising: asurge protection circuit; an overvoltage protection circuit coupled inseries with the surge protection circuit, the overvoltage protectioncircuit including: a relay configured to operate in a normally closedposition; a bridge rectifier; and a first circuit section coupled to thebridge rectifier and the relay, the first circuit section configured tocontrol operation of the relay based on an overvoltage detection signal;and a second circuit section coupled to the bridge rectifier and thefirst circuit section, the second circuit section configured to providethe overvoltage detection signal; wherein the first circuit section isconfigured to control the relay to be in an open state when theovervoltage detection signal is indicative of an overvoltage condition.15. The surge protective device of claim 14, wherein the first circuitsection comprises a first switching element and a second switchingelement configured as a Schmidt trigger.
 16. The surge protective deviceof claim 14, wherein the second circuit section comprises a plurality ofZener diodes.
 17. The surge protective device of claim 14, wherein theovervoltage protection circuit comprises an indicator circuit configuredto provide a visual indicator when the relay is in an open state.